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Nvidia has finally taken the wraps off its 64-bit Denver CPU core — and, well, let’s just say that the 64-bit Android race just got a lot more interesting. The Denver CPU will be available later this year in the Tegra K1 SoC, where you’ll get two Denver cores and a 192-core Kepler GPU. Nvidia says this will be the first 64-bit ARM chip for Android, and that it “completely outpaces” other ARM SoCs (including Apple’s monstrous A7 Cyclone). The Denver CPU is so beastly that it even beats out some PC-class chips (the low-end Haswell Celeron), while consuming much less power. The secret behind this performance boost is a novel technology called Dynamic Code Optimization.

First, let’s run through the Denver/K1 hardware specs. Denver is a 7-way superscalar in-order CPU core (it can execute seven instructions per clock cycle, which is a lot). Each core has 128KB of L1 instruction cache and 64KB of L1 data cache (both very large compared to the usual 32KB/32KB for a 32-bit ARM chip). In the 64-bit Tegra K1, there will be two Denver CPU cores sharing 2MB of L2 cache. The Denver CPU is expected to ship at 2.5GHz, which is rather fast. The Denver Tegra K1 will be pin-compatible with the current Cortex-A15 Tegra K1, making it easier for hardware makers to embrace the new chip when it arrives later this year.

Nvidia Denver CPU core, block diagram

Denver cores are very large, and there won’t be a quad-core variant (at least not in the short term). While the lack of a quad-core part might make for an uphill marketing battle — people still love their higher core counts — in reality a dual-core CPU should be more than capable of handling most workloads (most apps and games are still bottlenecked by single-threaded performance).

Nvidia Denver CPU core, Dynamic Code Optimization

Dynamic Code Optimization

Nvidia says Denver is explicitly designed to have “the highest single-core CPU throughput” — and while its 7-way superscalar design definitely accounts for a lot of that performance, the other trick up its sleeve is Dynamic Code Optimization.

Back in January we speculated that Nvidia might try something like Transmeta’s x86 emulation. As it turns out, Nvidia did try something rather weird and funky with the Denver core — but it has very little to do with x86. While Denver is an in-order chip, most modern CPU cores use out-of-order execution (OoOE) — where code is executed whenever it’s ready, rather than in the exact order laid out by the programmer — to increase the number of instructions executed per cycle. This works well, but it requires a significant chunk of silicon to actually perform the OoOE magic — and that silicon takes up die space and power. Instead, Denver uses Dynamic Code Optimization, which stores the most regularly executed code in a special 128MB main-memory Optimization Cache. This way, instead of having to fetch and decode instructions and data multiple times, the pre-digested and ready-to-go code can be run directly from the Optimization Cache. It’s a similar approach to how hybrid hard drives or SSD accelerators work.

While the actual process of storing code in the cache requires some additional processing power, Nvidia says the long-term performance gains are huge. In the case of Android tablets, where you probably only run a handful of apps, you could be running almost entirely from this optimized cache — in which case, the performance gains will be really quite significant.

In theory…

Android L

On paper, and in Nvidia’s internal benchmarks, the 64-bit Denver CPU core sounds rather exciting. The CPU handily beats every other ARM CPU on the market by some margin, and even does pretty well against the dual-core Celeron 2955U (Haswell). The 192-core Kepler GPU will probably be the fastest GPU on the market by some margin, too.

Perhaps most excitingly, though, the Denver Tegra K1 also looks like it will kick ass in reality, too. It’s important to note that the 64-bit Tegra K1 is the SoC of choice for Google’s upcoming Android L. Android L, which is due out towards the end of the year, is being developed specifically for the 64-bit Tegra K1 — and all signs point to the Nexus 9 tablet, which is probably an Android L launch device, having Nvidia’s 64-bit chip inside, too.

In the meantime, we’re still waiting to see what Qualcomm has planned for its ARMv8 64-bit CPU core. Apple caught everyone off guard when it was first to market with its custom-designed ARMv8 Cyclone CPU — and now Nvidia is proudly touting that it’ll be the first to market with a 64-bit Android CPU. It will be interesting to watch Qualcomm play catch-up when its 64-bit chip is finally ready to go (probably in 2015).

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